Process for the production of chlorine dioxide



July 16, 1935.

G. L. CUNNINGHAM PROCESS FOR THE PRODUCTION OF CHLORINE DIOXIDE Filed Feb. 2, 1954 @farai/'an C I INVENTOR ATTORNEYS 5 version of chlorine to chlorine dioxide.

Patented July 16, 1935 PROCESS Fon THE PRODUCTION F` CHLORINE proxima George Lewis Cunningham, Niagara Falls, N. i assigner to The Mathieson Alkali Works, Inc., l New York, N. Y., a corporation of Virginia Application February 2, 1934, Serial No. 709,482

8 claims. (ci. 28-7-205) This invention relates to improvements in the `production of chlorine dioxide, C102. More particularly, the invention comprisesY a combination of steps Vforming a cyclic process for the con- The process of the invention hasseveral` advantages. High efficiencies in the conversion of chlorine to chlorine dioxide can be attained. Chlorine, air and water are the only necessary raw materials, excepting fuel for heat and power. The process can be carried on to produce chlorine dioxide as the sole product without the production of waste products involving problems of loss and disposal.

The operation of the process of the invention depends upon a reaction of magnesium chloride `which distinguishes it from the chlorides of the alkaline earth metals and the alkali metals. This reaction is the thermal dissociation of magnesium chloride, in the presence of free oxygen, vto form `magnesium oxide, chlorine Vandl hydrochloric acid. For example, `'at a temperature `approximating 600-700 .C.,` magnesium chloride dihydrate 'disscciates in thevpresenceof free oxygeny to Vform magnesium oxide, chlorine and hydrochloric acid, the reaction being illustratedby the following Thisinvention takes advantage of this reaction peculiar to magnesium chloride to combine a `number'of steps in 'a unitary process." The relation of the dissociation step embodying this reaction to the combination is illustrated, diagrammatically, in Figure' l of the accompanying drawing, to which more detailed referenceis made below. l i

' The process of the invention comprises, asessential steps (l) separationof magnesium chloride and magnesium chlorate from a mixture of thesame, (2) dissociationof magnesium chloride fin, the presence of free oxygen to form magnesium oxide, chlorine and hydrochloric acid, (3) generation of a gas mixture including chlorine and chlorine dioxide by reaction of magnesium chlorate with hydrochloric acid (4) separation of chlorine from a gas mixture including chlorine and chlorine dioxide by reacting the gas mixture' with magnesium hydroxide and (5) chlorinating magnesium hydroxide, together with magnesium chloride and magnesium chlorate, to form a mixture of magnesium chlorate and magnesium chloride.` In the process of this invention, these steps are combined as follows: Magnesiumchloride from the lst'step is suppliedito the Znd'step and magnesium chloratefrom. the 1st stepis supplied to the 3rd step, hydrochloric acid from 'the 2nd step is supplied to the 3rd step, chlorine from the 2nd step is suppliedto the 5th step and magnesium hydroxide formed by hydration of magnesium oxide from the 2nd step is supplied to the 4th step, the gas mixture including chlorine and chlorine dioxide from the 3rd step is supplied to the 4th step, magnesium hydroxide formed by hydration of magnesium oxide from the 2nd step together with magnesium chloride and magnesium chlorate formed in the 4th step is supplied tothe 5th step, and magnesium chlorate and Ymagnesium chloride from the 5th step are supplied to the 1st step. Magnesium chloride formed in the 3rd step is with advantage returned to the 2nd step. Chlorine is supplied to the 5th step and chlorine dioxide is recovered from the 4th step. Again referring for the purpose of illus'- tration to Figure 1 of the accompanying drawing,

the `1st step is 'the separation A, the Zndstep is thedissociation,v the 3rd stepis the generation` the Lith'step is the separation Bi'and the 5th step is the chlorination.

`'Ihe'separation of magnesium chlorate from magnesium chloride in the 1st step of the combined operation may be carried out in any convenient manner. For example, this separation may be effected by fractional crystallization of the chloride from the chlorate, the latter being relatively more soluble. This separation is, howlever, with advantage effected as described in my Atio of water present to magnesium chloride and magnesium chlorate, H2O:MgCl2-|-Mg(C1O3)V2, does not exceed Aabout 6: 1, andthe resulting solid. mixture is subjected to countercurrent extraction For example, an

with acetone at a temperature below about C. After evaporation of theacetone for re-use in 'the extraction, magnesium chlorate containing not more than 10% (by weight) of magnesium chloride can be recovered from `the extract, Vthe balance of theY magnesium chloride being recovvered as the extraction residue.

In the second step ofthe combined operation, magnesium chloride is dissociated at a` temperature approximating 600700 C. in the presence of free oxygen, in the'rform of air for example.

vThe magnesiumchlorideis with advantage'sup- `exchange with hot furnace gases is advantageous inrthis connection. The dissociation may be carried out in any convenient manner, for example by passing the dihydrate through a kiln, a rotary kiln for example, countercurrent to hot furnace gases, from the combustion of coal or coke for example, containing excess air sufficient for the dissociation reaction. lThe consequent admixture o-f carbon dioxide with the chlorine formed in the 2nd step assists thechlorination in the 5th step. Y Magnesium oxideV is recovered as-a solid residue and the chlorine and nhydrochloric acid formed are evolved as gases. Hydrochloric .acid is separated from this gas mixture by cooling the gas mixture and contacting it with -water to recover the` hydrochloric acid as concentratedA aqueous hydrochloric acid in the conventional manner. The remaining gas mixture, including thechlorine formed in the dissociation, -is supe `plied to the 5th step;

,l The generation of aV gasrmixture including chlorine and chlorine dioxide in the 3rd step is effected by reacting the magnesium chlorate from the 1st step with hydrochloricV acid from the 2nd step. The magnesium chlorate supplied to the generationshould contain a minimum of magnesium chloride and in no event should the ,molecular ratio MgCl2:Mg(ClO3)2 exceed'2:1.

The magnesium chlorate is with advantage supv `plied to the generation Yas a concentrated solution in which' the molecular ratio Mg (ClOa) 2 H2O Vapproximates 1:4-6. "The generation reaction is with advantage carried out in an aqueous solu-V tion subjected Yto aeration. The volume of air used should besuch that the partial'pressure of chlorine dioxide in the resulting gas mixture does not substantially exceed 25-30 mm. of mercury at standard conditions. By so diluting the chlorine dioxide produced, danger of explosionV is minimized. The reaction efficiency is also improved. The following type equation illustrates the principal' reaction occurring:

Mgio)2+4Hc1 Mgo12+o12+2cio2+2n2o The following type equation illustrates a side re- Aaction which also occurs:

Using magnesium chlorate substantially free from magnesium chloride and an amount of hydrochloric acid exceeding that s'tochiometrically required by about 16%, as much as 85%-90% or more ofthe chlorine supplied to the generation as `magnesium chlorate is recovered as chlorine dioxide. The magnesium chloride solution pro- `duced in the generation reaction is with advantage supplied to the 2nd step with the magnesium chloride from the 1stV step, as described above. Any free hydrochloric acidi in Ythis solution is neutralized with partV of the magnesium oxide from the 2nd step before this solution is returned to the 2nd step.

The separation in thej4th step of chlorine from thegas mixture, including chlorine and chlorine dioxide, from the 3rd step is with advantage effected by reacting this gas mixture with substantially dry magnesium hydroxide formed by hydration of magnesium oxide from the 2nd step. 'I'he following type equation will'illustrate the reaction: i

Substantially all of the chlorine can thusbe separated from the gas mixture without loss of chlorine dioxide. This mode of operation is described in an application iiledFebruary 8, 1934,

`by George P. Vincent, Serial Number 710,326.

atmospheric pressure or with steam Vat temperatures upwards of 100 C. under atmospheric pressure. The n amount of magnesium Yhydroxide formed by hydration of the magnesium oxide produced in the 2nd step, after allowance for magnesium oxide normally required to neutralize the magnesium chloride solution produced in the 3rd step, exceeds that necessary for reaction inthe 4th step with thechlorine of the gas mixturein .cluding chlorine and chlorine dioxide, from the 3rd step. All or part of this'excess magnesium hydroxide'may be supplied to the 5th step through the 4th step or directly to the 5th step.

In the 5th Step,ichlorination ofthe magnesium hydroxide from the 2nd step, partly chlorinated t in the 4th step, is completed. The following type equation will illustrate the reaction: Y

6Mg on 2+.6c12a5Mgc12Jri/ig1o3)Henzo.

This Vchlorination `may be carriedV outin an acqueous solution or slurry inthe conventionalV manner. Chlorine from the 2nd step and` chlorine from an extraneous source are supplied to this chlorination, the amount of chlorine required to be supplied from an extraneous source corresponding to the amount of chlorine converted'to chlorine dioxide plus the losses incurred in the combined operation. This chlorination advantageously is controlled so that the chlorinated liquor produced contains a total of about 31% (by ForA example thishydration may be istl weight) of magnesium chloride and magnesium chlorate and so that the iinal temperature attained in the chlorination approximates C. After elimination of free chlorine and removal of sediment, in any conventional manner, this magnesium chloride-magnesium chlorate solution is supplied to lthe 1st step. Y Y

The invention is further illustrated bythe accompanying drawing, in the form of flow sheets, in which Figure l is a simplified diagram Aof the combination of steps forming the process of the invention and in which Figure 2 is a somewhat more detailed diagram representing a, process emf bodying the invention.. The same legends are used to designate the same steps in Figure' 1 and in Figure 2. Referring more particularly to lFigure 2, the separation of hydrochloric acid from the gas mixture evolved in the 2nd step is the separation C, the neutralization of free hydrochloric acid in the magnesium chloride solution from the 3rd step with magnesium oxide from the 2nd step is the neutralization and the hydration of magnesium oxide from the 2nd step for use in the 4th and 5th steps is the hydration.

This invention comprises essentially the combination of the five steps above recited and illustrated in Figure 1 of the accompanying drawing. The steps forming this combination, severally, include other inventions, some inventions made by me and some inventions made by others associated with me in this connection.

I claim: y

1. In the production of chlorine dioxide, the process which comprises separating magnesium chlorate and magnesium chloride from a mixture of the same, dissociating the separated magnesium chloride in the presence of free oxygen to form magnesium oxide, chlorine and hydrochloric acid, generating a gas mixture including chlorine and chlorine dioxide from the magnesium chlorate from the first-mentioned separation by reacting said magnesium chlorate with hydrochloric acid from said dissociation, separating chlorine from said gas mixture by reacting said gas mixture with magnesium hydroxide formed by hydration of magnesium oxide from said dissociation, chlorinating magnesium hydroxide formed by hydration of magnesium oxide from said dissociation together with magnesium chloride and magnesium chlorate formed in the second-mentioned separation to form a mixture of magnesium chlorate andl magnesium chloride and supplying that mixture to the first-mentioned separation.

2. In the production of chlorine dioxide, the process which comprises separating magnesium chlorate and magnesium chloride from a mixture of the same, dissociating the separated magnesiurn chloride in the .presence of free oxygen to form magnesium oxide, chlorine and hydrochloric acid, generating a gas mixture including chlorine and chlorine dioxide from the magnesium chlorate from the mst-mentioned separation by reacting said magnesium chlorate with hydrochloric acid from said dissociation, returning magnesium chloride formed in'said generation to said dissociation, separating chlorine from said gas mixture by reacting said gas mixture with magnesium hydroxide formed by hydration of magnesium oxide from said dissociation, chlorinating magnesium hydroxide formed by hydration of magnesium oxide from said dissociation together with magnesium chloride and magnesium chlorate formed in the second-mentioned separation to form a mixture of magnesium chlorate and magnesium chloride and supplying that mixture to the first-mentioned separation.

3. In the production of chlorine'dioxide, the process which comprises separating magnesium chlorate and magnesium chloride from a mixture of the same, dissociating the separated magnesium chloride in the presence of free oxygen to form magnesium oxide, chlorine and hydrochloric acid, generating a gas mixture including chlorine and chlorine dioxide from the magnesium chlorate from the first-mentioned separation by reacting said magnesium chlorate with hydrochloric acid 'from said dissociation, returning magnesium chloride formed in said generation to said dimociation after neutralizing unreacted hydrochloric acid with magnesium oxide from said dissociation, hydrating the remaining magnesium oxide from said dissociation, separating chlorine from said gas mixture by reacting said gas mixture with magnesium hydroxide from said hydration, chlorinating magnesium hydroxide from said hydration together with magnesium chloride and magnesium chlorate formed in the second-mentioned separation to form a mixture of magnesium chlorate and magnesium chloride and supplying that mixture to the first-mentioned separation.

GEORGE LEWIS CUNNINGHAM. 

